Radio receiver



Aug. 8, 193.9. H. M. L Ewls Er AL RADIO RBUEIVER original Filed oci. 4. `19:55

BY MlsoN cAwEl ATTORNEY Patented Aug. 8, 1939 UNITED STATE RADIO RECEIVER. Harold M. Lewis, Great Neck, and Madison Cawein, Ma

nhasset, N. Y., assignors to Hazeltine Corporation, a corporation oi Delaware Original application October 4, 1935, Serial No.

Divided and this application April 13,

- 1937, Serial N0. 136,534.

9 Claims.

This invention relates to audio-frequency modulated-carrier signal receivers and more particularly to methods of, and apparatus for, automatically controlling such receivers to provide improved operation.

The invention is especially directed to the automatic control of a receiver for reproducing sound from desired audio-frequency modulatedcarrier signals, but subject to the reception of l0 other signals'having components of predetermined characteristics, te modify the transmission characteristicsof the receiver when such other signals are received.

This application is a division of applicants copending application Serial No. 43,548, iiled October 4, 1935, Patent No. 2,137,123, dated November 15, 1938, wherein there is disclosed an improved television and` sound receiving system embodying novel and'improved means for the automatic control of the cathode-ray television reproducing tube, whereby the cathode ray is present with suilicient intensity to illuminate the screen only atA such times as a signal of the proper type and ofvsuilicient amplitude for reproducing an intelligible'signal is being received and proper scanning action is being provided;v

embodying also` improved means for automatically controlling the contrast of the picture detail in accordance with the amplitude of the received television carrier; and, further, em-

bodying improved automatic control means to prevent the reproduction of sound when undesired signals are present in the sound channel of the receiver. The invention of the present application is directed particularly to this latter feature. v

The automatic control of a sound-reproducing receiver in accordance with4 the reception of signals other than a desired selected signal isdesirable for various purposes. For example, in

certain cases it is desirable that the soundreproducing receiver be silenced when undesired signals having components of predetermined characteristics are received. For example, in

the reception of television programs in which alternate carriers have sound and vision modulations, during a tuning operation the sound channel of a combined television and sound receiver is tuned to alternately tune to a vision-modulated carrier. which would be reproduced as a harsh and disagreeable noise.

It is, therefore, a primary object of this invention to provide an improved method off, and means for, modifying the transmission characteristics of a sound-reproducing receiver when (Cl. Z50-20) signals other than the desired signals are re-v ceived.

A particular object of the present invention is to provide an improved method of, and means for, automatically controlling the reproduction of sound in a receiver designed for the reception of programs in a system in which alternate carriers are modulated by sound and vision to prevent undesirable effects of the vision-modulated signal in the sound channel of the receiver.

For a better understanding of this invention,

A together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.v

In accordance with the present invention, there is provided a receiver for reproducing sound from desired audio-frequency modulatedcarrier signals and subject to the reception of other signals having components of predetermined characteristics. The receiver comprises a single channel for selecting, amplifying, and detecting any one of a plurality of desired signals and discriminating against other signals. Means are provided for converting the detected signal into sound and further means are provided, responsive only to the presence in the sound-signal channel of a signal component which has one of the predetermined characteristics, to modify the transmission characteristics oi the receiver.

One satisfactory embodiment of the present invention comprises a combined sound and television receiver designed for the reception of alternate carriers modulated vby sound and vision frequencies. 'I'he reproduction of sound is controlled so as to prevent video frequencies from being reproduced by the sound channel of the receiver, as would otherwise result when the sound channel is tuned through a vision carrier. This is preferably accomplished by applying a voltage from the audio-frequency channel to a selecting, amplifying, and rectifying arrange-- ment to derive therefrom a negative biasing voltage only if and when video frequencies are present in the sound channel of the receiver. This biasing voltage may be appliedto the control grids of the audio-frequency ampliiler tubes, or other suitable tubes to silence the sound reproducer.

In the accompanying drawing, the single gure is a circuit diagram, partially schematic,-of a complete television receiving system embodying the present invention and including both visionand sound-modulated carrier receiving and reproducing channels.

Referring now more particularly to the drawing, theisystem there illustrated comprises a re' celver of the superheterodyne type including an antenna and ground system lt--IL connected to a radio-frequency ampliiier i2, which is connected in cascade with an oscillator-modulator I3, an intermediate-frequency amplier I4, a detector I 5, a video-frequency amplifier l5, and a cathode-ray tube il', constituting the visionfrequency channel o the receiver. The elements or components lt-i may all be of conventional well-known construction so that detailed illustration and description thereof is deemed unnecessary herein.

The cathode-ray tube it comprises the usual envelope I8 containing, in the order named, a cathode heater i9, a cathode iid, a main or videocontrol grid 2|, a screen 22, a first anode 23, a second anode 2li, andthe usual iiuorescent screen 25 at the end, of the tube. Line-frequency electro-static deflecting or scanning plates 26 are disposed Within the envelope It, and picture-frequency electromagnetic deiiecting or scanning coils 21 are disposed at opposite sides of the tube for deiiecting the beam in a direction normal to the direction of deflection effected by the plates 26. 'I'he output of the video-frequency amplifier is connected to the control grid 2| by way of the coupling condenser 28 and isolating resistance 28 for controlling the intensity of the cathode ray in accordance with the video frequencies, as in usual practice.

For developing saw-tooth voltage waves for the plates 26 and saw-tooth current Waves for the coils 21, to eiiect scanning action by the cathode y ray, a line-frequency generator 3U and a. picturefrequency generator 3| are provided. The out put of the video-frequency amplifier I6 is connected to these generators for controlling or operating them in proper synehronism with the scanning at the transmitter. The generators may be of any well-known or suitable design, such as, for instance, that described in United States Letters Patent No. 2,052,184, issued August 25, 1936, to Harold M. lewis on an application Serial No., 5,781, filed February 9, 1935.. The generators, however, are not limited to any. particular type and, furthermore, by virtue of the automatic fade-out control system, presently to be described in detail, the generators, instead of being continuously operative, as has heretofore been the practice, may be entirely controlled or driven by the output voltage of the video-frequency amplifier so as to operate only when proper synchronizing-frequency impulses are being supplied thereto.

For supplying operating potentials to the various electrodes oi' the tube l1, there is provided a voltage divider 32, adapted for connection to a suitable direct current power source, not shown, and the several electrodes are connected to appropriate taps on the divider. Certain of these taps, as, for instance, 32a, 32h, and 32e, for the control grid 2|, the screen 22, and the first anode 23, respectively, are preferably manually adjustable for regulating the initial bias voltages applied to these electrodes and for controlling the operation of the system, as will be presently more fully described. Current for the cathode heater `I! may be supplied in a conventional manner by a suitable circuit. not shown.

There is also provided a sound-frequency channel connected to the output of the oscillatoraluden modulator I3 and comprising, in cascade, an intermediate-frequency amplifier 33, a detector u, the audio-frequency ampliiier I5, and sound reproducer I6.

Since the system shown in the drawing, as thus 'far described, is, in general. conventional and well understood in the art, a detailed explanation of its general operation is deemed unnecessary. Briefly, however, the visionand sound-modulated carrier waves intercepted by the antenna lil-H are selected and amplified in the radio-ireqiicncyr amplifier I2 and supplied to the oscillator-modulator i3, Where the signals are converted to intermediate frequencies in the usual marmer.` The output of the oscillatormodulator is delivered to the intermediate-freouency amplifiers til and 33. The amplifier I t ls tuned to select a vision-modulated intermefilato-frequency carrier which, in systems where alternate carriers are modulated, respectively, by vision frequencies and sound frequencies, will be spaced of the order of one or more megacycles from the sound-modulated intermediate-frequency carrier, to which the amplifier 33 is tuned. The selected frequencies are amplified in the amplifiers i4 and 33 and supplied therefrom to the detectors i5 and Bt, respectively.

The detector It' produces the audio frequencies of modulation of the sound carrier and supplies them to the audio-frequency amplifier 35 whereby they are amplified and supplied in the usual manner to the loud-speaker 3G for reproduction,

It should be here noted that the detector I5 of the television channel is designed to develop in its output and deliver to the amplier I6 video frequencies corresponding to the envelope of a vision-modulated carrier, particularly a selfsynchronizing, lnegatively modulated carrier.

The video frequencies of modulation derived from the television carrier by the detector I5 are supplied to the vvideo-frequency amplier it wherein they are amplified and supplied in the usual manner to the control grid 2| of the cathode-ray tube and to the scanning generators 3l and 3|. Y

With the properpotentlals supplied to the electrodes of tube an electron beam is emitted from the cathode 2|! and its intensity is modulated or controlled by the grid 2|, in accordance with the video-frequency voltages impressed thereon. The screen t2 serves to control the average intensity of the beam in a manner hereinafter to be explained, while the ilrst anode 2l co-operates with the second anode 25 to accelcrate and focus the electron beam.'

Saw-tooth voltage waves are generated in the line-frequency generator 30 and applied to the plates 2% to produce an electrostatic field to defleet the beam in one direction, while saw-tooth current waves are generated in the picture-frequency generator 3| and are applied to the coils 21 to produce a magnetic eld of saw-tooth` wave form to deflect the beam in a direction normal to the deilectlon by the plates 26. The wellknown rectilinear scanning pattern is thus traced i on the screen by the beam. The generators 30 and 3| are preferably so adjusted as to operate mitter by the impulse components of the modulation frequencies supplied by the amplier, I6. Sultable'selective circuits, not shown, may be provided in the input circuits of the generators 30 32h on the voltage divider 32 through an isolating The -cathode 38 is connected to ground through a condenser 62. A resistor $6 is resistor d3.

connected across the rectifier 3l to develop the automatic fade-out control bias voltage output of this rectifier. An initial positive biasing potential'is applied to the screen 22 from the tap 32h on Athe voltage divider, through the path which includes the resistors 633 and dd.

The biasing potential applied to the screen 22 from the tap 32h is of suchmagnitude and polarity that the electron beam is normally insuillcient to illuminate the fluorescent screen. Whenever the generator 3@ is in operation,` however,

an additional bias voltage is developed by the rectifier 3l across the resistor t6, and this voltage is applied positively to the screenv 22 so as toV raise its potential, and permit the beam to become suilicieritlyl intense to illuminate the fluorescent screen.

The output voltage of the rectifier 3l may or may not be proportional to the amplitude of the received vision-modulated carrier wave, according to thedesign of the generator Si). As above mentioned, in this embodiment of the invention the generator 3B is preferably so designed that the amplitude of the periodic voltage developed therein and supplied to the rectifier i is substantially independent of the amplitude of the controlvoltage supplied to it from the video-frequency amplifier i6, unless such control voltage falls below a predetermined minimum, as disclosed in afore-mentioned Unitedl States Letters Patent No. 2,052,184. Hence, the input voltage to the rectifier 3l will besupplied only when the generator 30 is operating, and automaticfadeout control voltage will be developed for illuminating the screen 25 of the tube i1 only in the presence of a received signal and without appreciable gradation in the control of the screen illumination. It will also be appreciated that the farther removed the automatic fade-out control 1 detector is from the system input, the more in- 'dependentwill be the amplitude of the automatic fade-out control bias from the amplitude of the received carrier and thev more effective will be the protection of the cathode-ray tube by the automatic fade-out control.

For the purpose of controlling the contrast of the picture detail, a unidirectional bias voltage is derived by rectification of the intermediate-frequency carrier by the detector I5, and is applied to the control grids of one or more of the'amplifying tubes of the intermediate-frequency ampliiler i4. This automatic contrast control bias voltage is a negative voltage proportional tothe amplitude of the received carrier and its application to the tubes of the amplifier I4 controls their amplification so as to maintain the output of this amplifier within-a relatively narrow range for received signals of a wide range of intensities and above a predetermined value.

.Where the receiver just d\escribed is employed in systems in which alternate carrier waves have vision and sound modulation, respectively, and the receiver is properly tuned, the output of the amplifier 33 will be detected, amplified, and reproduced as sound in the manner afore-described. When, however, the receiver is being tuned through a range of such alternate carriers, visionand sound-modulation intermediate-frequency carriers will be present alternately in each of the amplifiers itand 33. As has been seen, the automatic fade-out control will prevent the screen 25 from being illuminated when a sound-modulated carrier is present in the amplifier IB, since such a carrier willnot have the proper frequency components of modulation for effecting scanning and operation of the automatic fade-out control.

By virtue of the arrangement provided by the present invention, the reproduction of noisy television signals by the sound reproducer is prevented when the vision-modulation frequencies are present in the sound channel of the receiver. This arrangement comprises amplifying, selecting, and detecting means, arranged to control the audio-frequency amplifier 535. A part of the audio-frequency output of the detector 36 is supplied through a coupling condenser d6 to the grid (il of a tube t5. In the plate circuit of the tube t5 is effectively included a selective circuit t3, which is tuned to the line-scanning frequency of the vision-modulated carrier, that is, the beatnote signal resulting from detection of the visionmodulated carrier and its sideband frequencies. The circuit d@ comprises a condenser 69 and an inductance 5U coupled to a coil ,Si connected in the plate circuit of tube Q5. The tuned circuit it is connected to a diode rectifier which may comprise an auxiliaryjanode and the cathode 53 of the tube d5, which, as illustrated, may be of the diode-triode type. The load circuit ofthe rectifier 52-53 comprises a resistor 56 and bypass condenser 55. Suitable operating potentials are applied to the plate y56 and grid 8l of the tube d5, as by batteries 5l and 58, respectively, and a blocking resistor 89 may be interposed in the connection to the grid fi'i.

When vision-modulated intermediate frequencies are present inthe amplifier 33 and are rectied by the detector 34, a part of the output of the detector is impressed upon the grid l1 .through the condenser @t and amplified in the triode section of the tube t5. Voltage of theA beat-note line-scanning frequency is then developed across the circuit 48 and rectied by the diode 52-5|3, producing a unidirectional biasing voltage across the resistor 54 in thewellknown manner. This biasing voltage is applied negatively, by way of the isolating resistor 35a, to the control grid of one or more of thetubes in the audio-frequency amplifier 3S and acts to suppress the audio-frequency amplifier 35 and to silence the loud-speaker 36.

-It will be apparent that, in the embodiment of the invention just described, a single sound istl like, and definitely to exclude mere dierences in signal intensity or amplitude. In the present instance, the beat notes comprise line-scanning frequencies which are developed by the beating of the television carrier and its sideband frequencies in the detector 34. The amplifier Il, selective circuit 48, and rectifier 52 thus comprise an arrangement which is selectively responsive to the beat notes, develops a control-bias voltage therefrom, and utilizes this voltage to modify the transmission characteristics of the receiver, specifically in the system described, to prevent the reproduction of sound.

Various other arrangements utilizing the pres- 1 ent invention in equivalent systems will be readily apparent to those skilled in the art. Obviously, the present invention may be employed in any system of which itis desired to modify the transmission characteristics when signals, other than a desired signal, are received'with sufficient amplitude to cause an undesired signal component of appreciable amplitude to be present in the output of the selecting and amplifying channel.

While there have been described what at present are considered the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications my be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modiiicationsas fall within the true spirit and scope of the invention.

What is claimed is: i

1. A receiver for reproducing sound from desired audio-frequency modulated-carrier signals and subject to the reception of undesired signals having periodically recurring modulation components of predetermined characteristics, comprising a single signal-translating channel for selecting, amplifying, and detecting any one of a plurality of said desired signals and discriminating against said other signals, means for converting the detected signal into sound, and means selectively responsive only to the presence in the detected output of said channel of a signal component corresponding to one of said undesired signal modulation components of predetermined characteristics for modifying' the transmission characteristics of said receiver.

2. A receiver for reproducing sound from desired audio-frequency modulated-carrier signals and subject to the reception of undesired signals having periodically recurring modulation components of predetermined characteristics, comprising a single signal-translating channel for selecting, amplifying, and detecting any one of a plurality of said desired signals and discriminating against said other signals, means for converting. the detected signal into sound, means selectively responsive only to the presence in the detected' output of said channel of a signal component corresponding to one of said undesired signal modulation components of predetermined characteristics for developing a control-bias voltage, and means for utilizing said voltage for modifying the transmission characteristics of said receiver.

3. A receiver for reproducing sound from desired audio-frequency modulated-carrier signals and subject to the reception of undesired signals having periodically recurring modulation components of predetermined characteristics, comprising a single signal-translating channel for selecting, amplifying, and detecting any one of a plurality of said desired signals and discrimandere inating against said other signals, means for converting the detected signal into sound, and means selectively responsive only to the presence in the detected output of said channel of a signal component corresponding to one of said undesired signal modulation components of predetermined characteristics for preventing the reproduction of sound by said receiver.

' 4. A receiver for reproducing sound from desired audio-frequency modulated-carrier signals and subject to the reception of undesired signals including predetermined modulation components, comprising a single Signat-translating channel for selecting, amplifying, and detecting any one of a plurality of said desired signals and incidentally developing in response to one of said undesired signal modulation component beat notes of a predetermined frequency, means coupled to said channel for converting the detected signal into sound, and means selectively responsive to said modulation component beat notes for modifying the transmission characteristics of said receiver.

5. A receiver for reproducing sound from desired audio-frequency modulated-carrier signals and subject to the reception of undesired signals including predetermined modulation components, comprising a 4single signal-translating channel for selecting, amplifying, and detecting any one of a plurality of said desired signals and 80 incidentally developing in response to one of said undesired signal modulatipn component beat notes of a predetermined frequency, means coupled to said channel for converting the detected signal into sound, and means selectively responsive to said modulation component beat notes for reducing the 'amplification in said channel.

6. A receiver for reproducing sound from desired audio-frequency modulated-carrier signals and subject to the reception of undesired signals including predetermined modulation components, comprising a single signal-translating channel for selecting, amplifying, and detecting any one of 'a plurality of said desired signals and incidentally developing in response to any one of said undesired signal modulation component beat notes of a predetermined frequency, means coupled to said channel for converting the detected signal into sound, means selectively responsive to said modulation component beat notes for developing a control-bias voltage, and means for utilizing said voltage for modifying the transmission characteristics of said receiver.

'7. A receiver for reproducing sound from desired audio-frequency modulatedwarrier signals and subject to the reception of undesired signals including predetermined modulation components, comprising a single signaltranslating channel for selecting, amplifying, and detecting any one of said desired signals and incidentally developing in response to one of said undesired signal modulation component beat notes of a predetermined frequency, means coupled to said channel for converting the detected desired signal into sound, and means selectively responsive to said modulation component beat notes for preventing the reproduction of sound by said receiver.

8 In an audio-frequency modulated-carrier receiver for reproducing sound subject to the reception of video-frequency modulated carriers having'synchronizing-frequency modulation components, means for selecting, amplifying, and detecting received waves'to derive therefrom audiofrequency modulated voltages, means for coning said. audio-frequency modulation voltages into sound. an amplifier connected to the output of said detector, a rectier, a selective circuit tuned to said synchronizing-frequency modulation components coupling said rectiiier to said amplifier, and means for applying the output voltage of said rectifier to said audio-frequency ampliiier to suppress the reproduction of sound.

HAROLD M. LEWIS. v 10 MADISON CAWEIN. 

